Process for producing nodular graphite iron



June 12, 1956 Filed Dec. 22, 1951 H. K. IHRIG PROCESS FOR PRODUCINGNODULAR GRAPHITE IRON 10 Sheets-Sheet l FERROUS METAL CONTAININGGRAPHITE YIELDING CARBON 2500 F EaT T MELT UNLESS ALREADY MEIJ'ED HALIDE0F NODULARIZING ELEMENT u, m, Mg, s, Bu, Rb, c

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PROCESS FOR PRODUCING MODULAR GRAPHITE IRON Filed Dec, 22', 1951 1.0Sheets-Sheet 8 B W M M. m m

June 12, 1956 H. K. IHRIG PROCESS FOR PRODUCING NODULAR GRAPHITE IRON 10Sheets-Sheet 10 Filed Dec. 22, 1951 BRINELL HARDNESS ELONGATION IN 2 IN.

PHYSICAL PROPERTIES (u a YIELD TENSILE 050W HEAT United States PatentPROCESS FOR PRODUCING NODULAR GRAPHITE IRON Harry K. Ihrig, Milwaukee,Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Application December 22, 1951, Serial No. 262,957

8 Claims. (Cl. 75-430) This invention relates generally to ferrous metalalloys and to processes for making them and specifically to theproduction of an as-cast ferrous metal containing spherular granule ofgraphite. The invention is also useful in providing a novel, simple andeconomical process for introducing into ferrous metal certain metalswhich have an influence upon the configuration of carbon inclusions inthe ferrous metal but which metals are ordinarily dimcult to introducebecause of their volatility, chemical activity and other properties.

A ferrous metal which is high in carbon, and has its carbon inclusionsin the form of graphite flakes is commonly termed cast iron. It is knownthat the physical properties of such ferrous metal, particularly thetensile strength, yield point and percent elongation, are im proved by(l) reducing the size of the graphite flakes, (2) distributing theflakes more uniformly throughout the metallic matrix, and (3) inducing aspecialized pattern of distribution of the graphite flakes. Because theflakes have flat leaf-like configurations which introduce majordiscontinuities into the metallic matrix, there is a limit to theimprovement of physical properties, particularly ductility, which can beachieved by any of the foregoing methods.

It has long been known that the physical properties of ferrous metalhigh in carbon, particularly the ductility, can be markedly improved byinducing the graphite inclusions to assume compacted shapes, sometimesin a form aptly described as nodular or spheroidal. When the graphiteinclusions are compacted, the metallic matrix is substantiallycontinuous and free of the major discontinuities inherent in matriceshaving flake or flake-like inclusions of graphite. The recognizedsuperior physical properties of so-called malleable cast iron (a kind ofiron made by a lengthy heat treating of white iron which has almost allits carbon in combined form) are attributable directly to the compactedform of the graphite inclusions although such inclusions (called tempercarbon) are not strictly nodular or spheroidal in shape, as the termsare used herein.

Cast ferrous metal, containing graphite-yielding carbon, which exhibitsa microstructure characterized to a substantial degree by compactedgraphite inclusions which are spherular has come to be known as nodulariron and, because it has superior physical properties, it is deemed ahighly desirable material for many structural purposes. Nodular ironsadvantage over gray cast or malleable cast iron lies not only in itsimproved physical properties, but also in the fact that nodular iron canbe cast directly from the melt and does not require heat treatment aftercasting. Whereas malleable cast iron, which has physical propertiessuperior to gray cast iron but generally inferior to nodular iron, canonly be made from white cast iron which has been subjected to a costly,time consuming and relatively complicated heat treatment.

The production of nodular iron, therefore, has drawn the attention ofinvestigator, with the result that several methods for its productionhave heretofore been proposed.

Patented June 12, 1956 The majority of these methods call forintroducing into molten iron containing graphite-yielding carbon one ormore substances capable of inducing the formation of spheroidal graphiteand then casting the molten metal to obtain nodular iron.

Among the substances heretofore mentioned for addition to molten ironcontaining graphite-yielding carbon to induce the formation ofspheroidal graphite without subsequent heat treatment after casting aremagnesium, calcium, strontium, barium, tellurium, cerium and zirconium.It has heretofore been proposed to introduce one or more of thesesubstances into the molten iron by bringing into contact with the molteniron either (1) the substance in elemental form, (2) an alloy of thesubstance, (3) a mixture of the substance with inert ingredients, or (4)a chemical compound of the substance with oxygen.

There are certain disadvantages to introducing these substances into themolten iron in any of the aforementioned forms.

For example, introducing magnesium in elemental form is impracticable aswell as hazardous because magnesium has a boiling point below themelting point of a eutectic iron carbon solution and will vaporize whenbrought into contact with the melt. The flashing of magnesium metal tovapor under such circumstances occurs with enough explosive violence toblow portions of molten iron from the melt.

Since the temperature of a ferrous metal melt previous to pouring isgenerally maintained around 1500 C., the same disadvantage accompaniesthe introduction of calcium, barium, tellurium, and cerium in elementalform since the respective boiling points of these elements in degreescentigrade are 1170, 1140, 1390 and 1400.

Introducing the spheroidal graphite inducing substances alloyed withmetals or nonmetals or mixed with inert materials, into the molten ironhas the disadvantage of not only introducing unwanted ingredients intothe iron, but in many cases of requiring the use of ingredients whichare costly or difficult to obtain. For example, it has heretofore beenproposed to use magnesium metal alloyed with one or more of thefollowing: silicon, nickel, aluminum, chromium, titanium, vanadium,molybdenum, manganese and copper.

The addition of magnesium alloyed with certain metals such as nickel orcopper is particularly undesirable when there is likelihood that thecast iron may later be used as scrap, since nickel and copper cannoteconomically be removed from the scrap metal. In some cases the alloyingmaterial may produce when added to the molten metal an elfect oppositeto the graphitizing effect of the spheroidal graphite inducingsubstance. Vanadium, for example, is one such material. Vanadium is apowerful carbide forming element and when added to gray iron willrestrain graphitization. Moreover, the majority of the alloying metalsproposed are strategic metals and in war times or in times of nationalemergency may be so strictly allocated as to be virtually unobtainable.

Bringing molten iron into contact with a compound consisting of an oxideof a spheroidal graphite inducing substance has heretofore beenmentioned as another method for producing nodular iron. For example, ithas been proposed to bring molten iron containing graphiteyieldingcarbon into contact with magnesia (magnesium oxide), with silicon orferrosilicon and perhaps small proportions of halides such as magnesiumchloride, calcium fluoride or magnesium fluoride present, attemperatures above 1100 C. However, this particular prior art processhas not been effective in producing nodular iron within temperatureranges ordinarily found in foundry practice; namely, 1100 C. to 1650 C.

Still another method heretofore proposed for making nodular ironconsists of bringing magnesia (magnesium oxide) into contact with molteniron at temperatures above 1650" C. Temperatures above 1650 C. are notnormally met with in iron foundry practice. For example, the normaltemperature range in the melt Zone of a cupola in an iron foundry liesbetween 1370 and 165 C. Temperatures above this range can only beattained by increasing the normal rate of fuel consumption. Suchincrease means not only higher fuel costs but also higher maintenancecosts because temperatures in the melt zone in excess of 1650 C. requirespecial refractory linings which cost more than linings suitable forlower temperatures. Furthermore, the higher the temperature the shorterthe life of the refractory lining and the more lining replacementsnecessary per ton of iron output.

7 The primary object of the present invention is to avoid thedisadvantages of the prior art through the provision of an improvedmethod for effecting the formation of spherular granules of graphite incast ferrous metal containing carbon.

Another object of the invention is to provide an im proved method ofadding to molten ferrous metal containing carbon the agents which inducethe formation of spherular granules of graphite in the ferrous metal asthe ferrous metal cools to the solid state.

Another object of the invention is to provide an improved method foreffecting a reduction in the proportion of flake graphite to spherulargraphite in cast ferrous metal containing carbon.

Another object of the invention is to provide an improved method forintroducing into molten ferrous metal certain alloying metals whichwould ordinarily be volatile at the temperature of the molten ferrousmetal.

Another object of the invention is to provide an improved method foravoiding an explosive condition when introducing into molten ferrousmetal an alloying agent containing a metal which would ordinarily bevolatile at a temperature below the temperature of the molten ferrousmetal.

Another object of the invention is to provide an improved method forincreasing the tensile strength, yield point, ductility and modulus ofelasticity of ferrous metal containing carbon.

Another object of the invention is to provide an improved method ofintroducing into molten ferrous metal nodularizing metals selected fromthe group consisting of lithium, sodium, magnesium, strontium, barium,rubidium and cerium.

Another object of the invention is to provide an improved method forproducing a nodular graphite cast ferrous metal which is substantiallyfree from nickel or copper in the as-cast state.

Another object of the invention is to provide an irnproved process forthe manufacture of nodular graphite ferrous metal which avoids theintroduction of nickelmagnesium and copper-magnesium alloys into theferrous metal.

Another object of the invention is to provide an improved method formaking nodular graphite cast ferrous metal in which the nodularizingreagent is distributed throughout the ferrous metal.

Another object of the invention is to provide an improved method ofmanufacturing a cast ferrous metal containing carbon, having at least aportion of the free graphite distributed throughout the as-cast ferrousmetal in the form of substantially spherular granules, wherein heattreatment of the ferrous metal after casting is avoided.

Another object of the invention is to provide an improved method formaking nodular graphite cast ferrous metal, which method is economicaland simple to perform.

Another object of the invention is to provide an 1mproved cast ferrousmetal containng carbon which has physical properties in the as-castcondition supenor to the physical properties of ordinary gray cast ironin the as-cast condition.

Another object of the invention is to provide an improved cast ferrousmetal containing carbon which has a tefnsile 1strength, yield point andductility similar to that o stee.

Another object of the invention is to provide an improved cast ferrousmetal containing carbon which has a modulus of elasticity substantiallyequal to or greater than that of malleable iron.

Another object of the invention is to provide an improved cast ferrousmetal containing carbon but substantially free from nickel and copper,which cast ferrous metal exhibits physical properties substantiallyequal or superior to prior art cast irons containing nickel or copper.

Another object of the invention is to provide an improved method foradding to molten ferrous metal containing carbon certain substancescapable of inducing the formation of spherular granules of graphite inthe ferrous metal as the metal solidifies without introducing oxygeninto the metal.

The present invention proposes to achieve the aforesaid objects bybringing together molten ferrous metal containing graphite-yieldingcarbon, a sufficient quantity of a halide of a spherular graphiteinducing element selected from the group consisting of lithium, sodium,magnesium, strontium, barium, rubidium and cerium to inducenodularization when reduced, and a reducing agent capable of reducingthe halide, and then solidifying the molten metal While the inducingelement is effective in promoting the formation of spherular graphite.

Other objects and advantages will be apparent from the specification andthe accompanying drawings.

In the drawings:

Fig. 1 is a flow sheet generally illustrating the process of theinvention, a detailed explanation of which is to be found hereinafter inthe specification;

Fig. 2 is a photomicrograph (X) of a section of a sample of nodular ironmade by the process of the present invention in which magnesium chlorideis used as the source of the spherular graphite inducing substance;

Fig. 3 is a photomicrograph (X100) of a section of a sample of nodulariron made by the process of the present invention in which sodiumchloride is used as the source of the spherular graphite inducingsubstance;

Fig. 4 is a photomicrograph (X100) of a section of a sample of nodulariron made by the process of the present invention in which magnesiumchloride and sodium chloride are the source of the spherular graphiteinducing substances;

Fig. 5 is a photomicrograph (X100) of a section of a sample of nodulariron made by the process of the present invention in which lithiumchloride is the source of the spherular graphite inducing substance;

Fig. 6 is a photomicrograph (X100) of a section of a sample of nodulariron made by the process of the present invention in which bariumchloride is the source of the spherular graphite inducing substance;

Fig. 7 is a photomicrograph (X100) of a section of a sample of nodulariron made by the process of the present invention in which strontiumchloride is the source of the spherular graphite inducing substance;

Fig. 8 is a photomicrograph (X100) of a section of a sample of nodulariron made by the process of the present invention in which misch metalchloride (approximately 50% cerium chloride) is the source of thespherular graphite inducing substance;

Fig. 9 is a photomicrograph (X100) of a section of a sample of nodulariron made by the process of the present invention in which rubidiumchloride is the source of the spherular graphite inducing substance;

Fig. 10 is a photomicrograph (X100) of a sectlon of a sample of nodulariron made by the process of the present invention in which sodiumbromide is the source of the spherular graphite inducing substance;

Fig. 11 is a photomicrograph (X100) of a section of a sample of nodulariron made by the process of the present invention in which sodium iodideis the source of the spherular graphite inducing substance;

Fig. 12 is a photomicrograph (X100) of a section of a sample of nodulariron made by the process of the present invention in which sodiumfluoride is the source of the spherular graphite inducing substance;

Fig. 13 is a photomicrograph (X100) of a section of a sample of nodulariron made by the process of the present invention in which magnesiumfluoride is the source of spherular graphite inducing substance;

Fig. 14 is a photomicrograph (X500) of a section of a sample of nodulariron made by the process of the present invention illustrating in moredetail the structural form of the spherular granules of graphiteobtained in the ascast iron;

Fig. 15 is a table giving specific examples of the approximatepercentages by weight of certain ingredients (the ingredients beingidentified by their chemical symbols), and the values of certainquantities involved, in the practice of this invention; and

Fig. 16 is a table giving the physical properties of the iron madeaccording to the process of the invention using the percent ingredientsspecified in the table of Fig. 15.

The present invention comprehends a process for making a ferrous metalcharacterized to a substantial degree by a matrix containing spherulargranules of graphite as exemplified in the photomicrographs shown inFigs. 2 to 14. The invention utilizes the spherular graphite inducingeffect of certain metallic elements when introduced into a moltenferrous metal containing graphite-yielding carbon, but instead. ofintroducing the element in uncomn bined form as a free chemical element,or as an element alloyed or mixed with other materials, or as a metallicoxide, this invention contemplates bringing the element in the form of ahalide of the element into contact with the molten bath of ferrous metalin the presence of a suitable reducing agent consisting essentially ofan element selected from the group consisting of calcium, potassium, andbarium. In this way the spherular graphite inducing element can beintroduced into the metal (1) without the explosive effects incident tointroduction in elemental form, (2) without introducing unwanted orundesirable substances into the metal, and (3) without introducing aspherular graphite inhibitor such as oxygen.

Elements which have shown themselves to be satisfactory spherulargraphite inducers when brought together in the form of halides with abath of molten ferrous metal containing graphite-yielding carbon arelithium, sodium, magnesium, strontium, barium, rubidium and cerium. Thehalides of the foregoing elements will at times hereinafter be referredto as nodularizing halide compounds. Each of the elements mentioned,when introduced otherwise than as a halide, have recognized nodularizingeffects, except for sodium Whose nodularizing action has not heretoforebeen known. The discovery that sodium halides are excellent nodularizinghalide compounds is an important aspect of this invention particularlyin view of the cheapness and ready availability of sodium chloride(common salt).

The reducing agent employed in conjunction with the nodularizing halidecompound must be one active at the temperature of the molten metal bathto cause the nodularizing element to be released to perform its intendedfunction. One reducing agent having the properties desired is metalliccalcium which may be conveniently supplied as calcium silicide (anintermetallic composition containing about calcium). The calcium appearsto combine with the halogen radical to render the nodularizing elementavailable for performing its nodularizing function. The calcium halidethus formed (and-the silicon oxides formed from silicon which does notenter the metallic bath) appear as a floating slag.

Other reducing agents which may be employed are potassium and barium,the latter being conveniently supplied as barium silicide. Potassium hasbeen found useful in causing the nodularizing element magnesium to bereleased from its chloride to perform its nodularizing function. Bariumhas been found useful in causing both the nodularizing elementsmagnesium and sodium to be released from their chlorides for the samepurpose.

The nodularizing halide compound may be mixed with the reducing agentand molten metal containing carbon poured over the mixture which haspreviously been placed in a ladle, or the mixture may be added to thestream of molten metal as it is poured. In the table of Fig. 15, thecolumn headed Pouring Temperature gives the temperature of the moltenferrous metal (base metal) at the instant it is brought into contactwith the halide and reducing agent.

After the slag forms it is usually separated from the melt beforeobtaining the nodular iron casting. In a cupola or other furnace thisseparation may be accomplished according to the usual practice withoutactually removing slag from the melt, by tapping the melt below the slaglevel. If the nodular iron is made in a ladle, a teapot or bottom pourladle may be employed to separate the slag from the molten metal at thetime of pouring.

Soon after the halide has been reduced the melt should be poured so asnot to lose the nodularizing effect of the inducing element since thenodularizing elfect is found to decrease as the time between reductionand pouring is extended. The length of interval between treatment andpouring, in which interval the nodularizing effect will not appreciablydiminish, appears dependent upon the quantity of nodularizing halidecompound and reducing agent introduced into the molten metal. It hasbeen found, for example, with a 400 pound heat of pig iron (base ironcontaining carbon 3.35%, silicon 0.84%, phosphorus 0.055%, sulfur 0.028%and manganese 0.017%, and the remainder iron) that when the melt Waspoured eight minutes after treatment (the percentage additions by weightbeing magnesium chloride 1.05%, sodium chloride 1.05% and calciumsilicide 4.70%), the iron as cast was approximately ninety-five percentnodular, the remaining five percent showing modified flakes. When pouredeleven minutes after treatment the iron as cast was approximately fiftyto sixty percent nodular. Pouring fourteen minutes after treatment gavean iron, as cast, approximately fifteen to twenty percent nodular, andwaiting an additional half minute resulted in an iron only approximatelyten percent nodular.

Iron produced by this process has physical properties of a modulus ofelasticity much superior to the base iron. As an example of the greatlyimproved physical properties that can be realized with this process, agray iron having a tensile strength of 12,300 p. s'. i., a yield pointof 7,000 p. s. i., and an elongation of 1% was treated according to thisprocess to produce an iron, as cast, having a tensile strength of 78,200p. s. i., yield point of 43,000 p. s. i. and an elongation of 12.5%. Themodulus of elasticity before treatment was approximately 15,000,000 p.s. i., Whereas after treatment the modulus of elasticity wasapproximately 27,000,000 p. s. i., a figure comparable to malleableiron.

Tensile strengths exceeding 105,000 p. s. i. have been measured formaterials made in accordance with this invention, although the averageof tensile strengths for the specific examples listed in Fig. 16 is wellover 70,000 p. s. 1.

The halides of the spherular graphite inducing elements include thechlorides, bromides, iodides and fluorides. Sodium chloride, sodiumbromide, sodium iodide and sodium fluoride when introduced into molteniron containing carbon and reduced by calcium silicide produced ironcharacterized by the presence of sperular granules of carbon, as shownin the photornicrographs of .Figs. 2,

10, 11 and 12 respectively. Sodium .chloride, which is ordinary .tablesalt, .is inexpensive and easily obtained regardless of war times ornational emergency. Ma nesium chloride is likewise inexpensive andreadily available. For these reasons the chlorides of magnesium andsodium are preferred to the bromides, iodides and fluorides of theseelements and to the halides of lithium, barium, strontium, cerium andrubidium.

It has been found that calcium alone will not produce nodular ironunless an inordinate proportion (50 percent or more) of nickel ispresent. The ostensible function of calcium in the process of theinvention is to combine with the halogen to free the nodularizingelement.

Mixing two halides such as sodium chloride and magnesium chloride andintroducing the mixture into the molten metal for reduction by calciumsilicide has been found as eflicacious in producing nodular graphite asintroducing one or the other of the halides alone and eifecting thesingle reduction.

The process of this invention may be illustrated by a flow sheet or flowdiagram, as shown in Fig. 1. The flow diagram presupposes operationconforming to ordinary foundry practices and equipment, and indicatesthat the ferrous metal containing graphite-yielding carbon is usuallymelted as a first step. Metal already moiten, as from a blast furnance,cupola, or the like, may, of course, be used as well. The diagramfurther assumes that treatments not indicated, such as adjustments ofcarbon or silicon content, elimination of oxygen, reduction of sulfur orphosphorus content, addition of alloying agents, employment of chilltechniques in casting or others may or may not be performed atappropriate stages of the process without alteration of its maincharacter and pupose.

'The process of making nodular iron according to this invention bybringing together molten ferrous metal containing graphite-yieldingcarbon, the halide of a spherular graphite inducing element, and asuitable reducing agent is illustrated by the following examples:

Example N0. 1

A charge of pig iron (base iron) containing carbon 4.03%, silicon 0.85%,phosphorus 0.050%, sulfur 0.023%

and manganese 0.15% was melted in the furnace at A sample machined fromthe final nodular casting had the following physical properties as cast:

Tensile strength p. s. i 65,600 Yield point p. s. i 41,500 Elongation in2 inches percent 16.5

'Brinell hardness 159 A comparison of the physical properties of theiron before and after treatment according to the process of thisinvention, as exemplified by the preceding example, shows an increaseafter treatment in both tensile strength and yield point of almost 600%,and an increase in ductility to 16.5% from a ductility of zero percentfor untreated material.

Example N0. 3

A charge of pig iron (base iron) containing by weight, as a percentageof the charge, carbon 4.34%, silicon 0.73%, phosphorus 0.045%, sulfur0.023% and manganese 0.10% was melted in an induction furnance. To themolten iron in the furnace was added 0.7% calcium silicide .to.deoxydize the iron. However, the addition of calcium silicide is notessential :if the iron does' not need deoxydizing. The molten metal wasthen poured at 2675 F. over a mixture of 3.5% magnesium chloride, whichwas essentially anhydrous, and 3.5% calcium silicide previously placedin the bottom of a heated laddle. After the reaction had taken place theslag was removed and the molten metal cast into a mold.

A sample of the base iron before treatment had a tensile strength ofabout 12,000 ,p. s. i., yield point of about 7,500 p. s. i. and zeropercent elongation.

A sample machined from the casting showed the following physicalproperties, as cast:

photomicrograph of Fig. 2, has all of the graphite in nodular form andhas a matrix of about 50% ferrite and 50% pearlite.

Example N0. 3

A charge of pig iron (base iron) containing by weight, as a percentageof the charge, carbon 4.20%, silicon 0.75%, phosphorus 0.35%, sulfur0.039% and manganese 0.10% was melted and to the charge was added 0.69%calcium silicide to deoxydize the iron. The molten metal was poured at atemperature of 2800 F. over a mixture of 4.41% of sodium chloride (whichwas essentially anhydrous) and 6.63% calcium silicide in a heated ladle.After removing the slag the contents of the ladle were cast into a mold.

A sample of the base iron before treatment had a tensile strength ofabout 12,000 p. s. i., yield point of about 7,500 p. s. i. and zeropercent elongation.

A sample machined from the casting had the following physicalproperties, as cast:

Tensile strength p. s. i 90,200 Yield point p. s. i 85,000 Elongation in2 inches -percent 3 Brinell hardness 207 Example N0. 4

A charge of pig iron (base iron) containing by weight, as a percentageof the charge, carbon 3.84%, silicon 0.66%, phosphorus 0.060%, sulfur0.026% and manganese 0.13% was melted and to the melt was added 0.70%calcium silicide to deoxydize the iron. The molten metal was then pouredat a temperature of .2700" F. over a mixture of 3.99% sodium chloride,0.22% magnesium chloride and 5.26% calcium silicide. (Both the sodiumchloride and the magnesium chloride were essentially anhydrous.) Afterremoving the slag from the metal the contents of the ladle were castinto a mold.

A sample of the base iron before treatment had a tensile strength ofabout 12,000 p. s. i., yield point of about 7,500 p. s. i. and zeropercent elongation.

A sample machined from the casting had the following physicalproperties, as cast:

Brinell hardness 163 The microstructure of this sample, as shown in thephotomicrograph of Fig. 4, is approximately nodular. The matrix isferrite.

Example N0.

A charge of pig iron (base iron) containing carbon 3.88%, silicon 0.67%,phosphorus 0.025%, sulfur 0.029% and manganese 0.11% was melted and tothe charge was added 0.70% calcium silicide to deoxydize the iron. Themolten metal was poured at a temperature of 2700 F. over a mixture of3.25% anhydrous lithium chloride and 6.36% calcium silicide in a heatedladle. After removing the slag the molten metal was cast into a mold.

A sample of the base iron before treatment had a tensile strength ofabout 12,000 p. s. i. and zero elongation.

A sample machined from the casting had the following physicalproperties, as cast:

Tensile strength p. s. i 95,600 Elongation in 2 inches .percent Brinellhardness The microstructure of this sample, as shown in themicrophotograph of Fig. 5, is predominantly nodular.

The matrix is almost entirly ferrite.

Example N0. 6

A charge of base iron containing by weight, as a percentage of thecharge carbon 1.09%, silicon 0.16%, phosphorus 0.06%, sulfur 0.008% andmanganese 0.35% was melted, and to the charge was added calcium silicide0.66% to deoxydize the iron. The molten metal was poured at atemperature of 2900 F. over a mixture of anhydrous magnesium chloride1.05%, anhydrous sodium chloride 1.05% and calcium silicide 4.00% in aheated ladle. After removing the slag the contents of the ladle werecast into a mold.

A sample machined from the casting contained spherular granules ofgraphite and had the following physical properties, as cast:

Brinell hardness The process of this invention may be practicedvariously with the several nodularizing halide compounds and reducingagents identified in the table of Fig. 15, to give the improved physicalproperties shown in the table of Fig. 16. Each heat in the tablerepresents base materials which initially had tensile strengths around12,000 p. s. i., yield points around 7,500 p. s. i., and elongationsfrom 0 to 1% before treatment, and which were treated in accordance withthis invention generally following the practices described in theforegoing detailed examples. The physical properties listed were thoseascertained by actual measurements.

The amounts and percentages given in the foregoing examples and in theexamples in the table of Fig. 15 may be varied considerably withoutdeparting from the scope of the invention so long as the amounts andpercentages are sufficient to produce a ferrous metal, as cast, having amicrostructure characterized by a matrix containing spherular granulesof graphite.

The term as cast, as used herein, represents the condition of a metalmass which has been brought from a liquid state above its melting pointto a cold solidified state by cooling at a rate typical of the rate ofcooling of castings in normal foundry practice.

The term ferrous metal containing graphite-yielding carbon, as usedherein, defines a ferrous alloy which has suflicient carbon to form,upon solidification of the metal from the liquid state and upon cooling,a matrix microstructure characterized by free carbon inclusions in thecold metal. This ferrous metal is the metal referred to as Base metal inthe table of Fig. 15.

The range of carbon content which complies with the foregoing definitionis dependent upon substances in the alloy other than iron and carbon.For example, presence of silicon and certain other substances has animportant bearing upon the readiness with which c'ementite of theferrous metal will decompose to yield ferrite and free carbon. Suchsubstances, termed graphitizing agents, act to extend the lower end ofthe range of carbon content within which this invention is usefullyoperative well down into if not throughout the range of the so-calledhyper-eutectoid steels.

The upper end of the range of carbon content of ferrous metal high incarbon is set by convenience in melting and utility of the materialproduced, and reaches up to and beyond the upper limits of carboncontent of high carbon pig iron. In the absence of substantialproportions of substances such as sulfur, phophorus, oxygen, and thelike, and special alloying agents, this range will extend approximatelyfrom 0.8% carbon to 6.7% carbon but the limits of usefulness of theinvention may extend outside of this range, as for example, when asubstantial proportion of nickel, chromium, manganese or other alloyingagents is present.

So-called high sulfur iron may be converted into nodular iron by theprocess of this invention, provided the iron has sufficientgraphite-yielding carbon, if the iron is first desulfurized by any wellknown method such as adding sodium carbonate or calcium oxide to themelt.

It will be evident that by the aforementioned process a number ofnodular iron alloys may be made which have a microstructurecharacterized by a matrix containing spherular granules of graphite andthat these alloys may retain in the as-cast condition one or more of thefollowing elements, lithium, sodium, magnesium, strontium, rubidium,barium and cerium.

Since the examples of the processes given are illustrative only, theinvention is not to be limited thereto but may include equivalents,modifications and variations coming within the scope of the appendedclaims.

It is claimed and desired to secure by Letters Patent;

1. The process for obtaining from a molten ferrous metal containinggraphite yielding carbon a ferrous metal characterized in the solidstate by the presence of spherular granules of graphite therein,comprising: bringing together said molten ferrous metal, a halide of aspherular graphite inducing element selected from the group consistingof lithium, sodium, magnesium, strontium, barium, rubidium and cerium,and an agent capable of reducing said halide in said molten ferrousmetal, said agent consisting essentially of an element selected from thegroup consisting of calcium, barium, and potassium; and solidifying saidmolten ferrous metal while said spherular graphite inducing element iseffective in inducing the formation of spherular graphite.

2. The process for obtaining from a molten ferrous metal containinggraphite yielding carbon at ferrous metal characterized in the solidstate by the presence of spherular granules of graphite therein,comprising: bringing together said molten ferrous metal, magnesiumchloride, and a reducing agent consisting of potassium, said reducingagent being capable in said molten ferrous metal of reducing saidhalide; and solidifying said molten ferrous metal while said magnesiumis effective in inducing the formation of spherular graphite.

3. The process for obtaining from a molten ferrous metal containinggraphite-yielding carbon a ferrous metal characterized in the solidstate by the presence of spherular granules of graphite therein,comprising: bringing together said molten ferrous metal, lithiumchloride, and a reducing agent capable in said molten ferrous metal ofreducing said chloride, said reducing agent consisting of a compound ofcalcium and silicon; and solidifying said molten ferrous metal whilesaid lithium is effective in inducing the formation of spherulargraphite.

4. The process for obtaining from a molten ferrous metal containinggraphite-yielding carbon a ferrous metal characterized in the solidstate by the presence of spherular granules of graphite therein,comprising: bringing together said molten ferrous metal, bariumchloride, and a reducing agent capable in said molten ferrous metal ofreducing said barium chloride,,said reducing agent consisting of acompound of calcium and silicon; and solidifying said molten ferrousmetal while said barium is effective in inducing the formation ofspherular graphite.

5. The process for obtaining from a molten ferrous metal containinggraphite-yielding carbon 2. ferrous metal characterized in the solidstate by the presence of spherular granules of graphite therein,comprising: bringing together said molten ferrous metal, ceriumchloride, and a reducing agent capable in said molten ferrous metal ofreducing said cerium chloride, said reducing agent consisting of acompound of calcium and silicon; and solidifying said molten ferrousmetal while said cerium is effective in inducing the formation ofspherular graphite.

6. The process for obtaining from a molten ferrous metal containinggraphite-yielding carbon a ferrous metal characterized in the solidstate by the presence of spherular granules of graphite therein,comprising: bringing together said molten ferrous metal, magnesiumchloride, and a reducing agent consisting of an intermetallic compoundof calcium and silicon, said reducing agent being capable in said moltenferrous metal of reducing said magnesium chloride; and solidifying saidmolten ferrous metal while said magnesium is effective in inducing theformation of spherular graphite.

7. The process for obtaining from a molten ferrous metal containinggraphite-yielding carbon a ferrous metal characterized in the solidstate by the presence of spherular granules of graphite therein,comprising: bringing together said molten ferrous metal, sodiumchloride, and a re- I12 ducing agent consisting of an intermetalliccompound of calcium and silicon, said reducing agent being capable insaid molten ferrous metal of reducing said sodium chloride; andsolidifying said molten ferrous metal while said sodium is effective ininducing the formation of spherular graphite.

8. The process for obtaining from a molten ferrous metal containinggraphite-yielding carbon a ferrous metal characterized in the solidstate by the presence of spherular granules of graphite therein,comprising: bringing together said molten ferrous metal, chlorides ofspherular graphite inducing elements consisting of magnesium and sodium,and a reducing agent consisting of a compound of calcium, said reducingagent being capable in said molten ferrous metal of respectivelyreducing said magnesium chloride and said sodium chloride; andsolidifying said molten ferrous metal While said magnesium and sodiumare effective in inducing the formation of spherular graphite.

References Cited in the file of this patent UNITED STATES PATENTS906,009 Goldschmidt Dec. 8, 1908 2,036,576 Hardy Apr. 7, 1936 2,154,613Guthrie Apr. 18, 1939 2,485,760 Millis et al. Oct. 25, 1949 2,488,511Morrogh Nov. 15, 1949 2,527,037 Smalley Oct. 24, 1950 2,552,204 MorroghMay 8, 1951 2,662,820 Crome Dec. 15, 1953

1. THE PROCESS FOR OBTAINING FROM A MOLTEN FERROUS METAL CONTAININGGRAPHITE YIELDING CARBON A FERROUS METAL CHARACTERIZED IN THE SOLIDSTATE BY THE PRESENCE OF SPHERULAR GRANULES OF GRAPHITE THEREIN,COMPRISING: BRINGING TOGETHER SAID MOLTEN FERROUS METAL, A HALIDE OF ASPHERULAR GRAPHITE INDUCING ELEMENT SELECTED FROM THE GROUP CONSISTINGOF LITHIUM, SODIUM, MAGNESIUM, STRONTIUM, BARIUM, RUBIDIUM AND CERIUM,AND AN AGENT CAPABLE OF REDUCING SAID HALIDE IN SAID MOLTEN FERROUSMETAL, SAID AGENT CONSISTING ESSENTIALLY OF AN ELEMENT SELECTED FROM THEGROUP CONSISTING OF CALCIUM, BARIUM, AND POTASSIUM; AND SOLIDIFYING SAIDMOLTEN FERROUS METAL WHILE SAID SPHERULAR GRAPHITE INDUCING ELEMENT ISEFFECTIVE IN INDUCING THE FORMATION OF SPHERULAR GRAPHITE.